A conventional pyroelectric IR-sensor essentially comprises a pyroelectric light receiving element, a substrate or base plate of alumina for supporting the pyroelectric light receiving element in a manner that this pyroelectric light receiving element is spaced from the substrate by spacing pads, and provided with a wiring pattern and a resistor formed on the surface thereof, and an FET chip mounted on the substrate.
The method of manufacturing the above-mentioned pyroelectric IR-sensor will be described hereinafter.
At first, a substrate is provided by forming a wiring pattern and a resistor by silk screen printing and baking on an alumina plate molded in a predetermined shape. Next, a FET chip is soldered onto the substrate. Then, a conductive paste is put on the substrate, the top of the paste is flattened and the paste is suitably hardened to provide spacing pads. Finally, a pyroelectric light receiving element is bonded on the spacing pads.
Since the pyroelectric light receiving element serves to sense changes in temperature in response to infrared rays, this element must be thermally isolated from other components.
To realize this, in the above-described conventional pyroelectric IR-sensor, the pyroelectric light receiving element is spaced from the substrate by the spacing pads and is thus thermally isolated therefrom.
Since heat is transferred through the spacing pads, however, the thermal isolation is insufficient. Further, since it is extremely difficult to form the spacing pads with a high precision, unevenness occurs in the thermal isolation of the pyroelectric light receiving element. This causes unevenness in the characteristics of the pyroelectric light receiving elements. Furthermore, an unbalance occurs in the transfer of heat through the spacing pads which support the pyroelectric light receiving element. This causes the production of noise due to an unbalanced voltage.
In addition, it takes a relatively long time in the process to form the spacing pads. This constitutes an obstacle to improvement in productivity.